It sounds like his underlying issue that began his drinking was depression. I can see how that would cause him to feel he doesn't benefit when he attends a group setting for supporting those who have the problem and want to stay on the path of living their lives sober. (usually it works best for those who need social guidance and stimulation)

He probably did not react to your request for divorce because it may be something he no longer has to worry about. Depression is a beast to deal with and for some functioning at all takes a lot. He should see a doctor and get a physical and blood tests to make sure he doesn't have any health issues that contribute to his depression. Sometimes a vitamin deficiency can be a contributing factor. Then he will need to experiment with medications to see what combination helps and that does require patience.

It's very hard to be in a relationship with someone who is challenged. You certainly have been patient and hopeful for a long time. You will benefit from therapy yourself, especially since you tried so hard to be patient. Depression is hard on everyone in the family.